There are two intravenous spasmolytics available for CT colonography; hyoscine butylbromide and glucagon hydrochloride. Both produce hypotonia in smooth muscle within the colonic wall and are used widely to improve distension during double contrast barium enema. However, while both agents have been shown to improve patient perception during barium enema, only hyoscine butylbromide reliably improves distension (Goei et al. 1995; Bova et al. 1993). As a result, it is widely utilized for barium enema across Europe (hyoscine butylbromide is not licensed for use in the USA).
The use of spasmolytics prior to CT colonography has been widely investigated. In one randomised study (Taylor et al. 2003), intravenous administration of 20 mg hyoscine butylbromide immediately prior to gas insufflation was associated with significantly improved distension in all colonic segments proximal to the sigmoid. Moreover, for all segments combined, the colon was over six times more likely to be adequately distended compared to using no spasmolytic. Interestingly, there was no additional benefit gained by increasing the dose to 40 mg. A smaller study (Bruzzi et al. 2003) also showed significantly improved transverse and descending colonic distension in patients given hyoscine butylbromide, but only in patients with diverticu-
lar disease. The authors postulated that hyoscine butylbromide might relieve diverticulosis related spasm. More recently, data has been presented comparing hyoscine butylbromide and glucagon hydrochloride to no spasmolytic (Rogalla et al. 2004b). These authors found that both spasmolytics conveyed benefit, an effect most marked when using hyoscine butylbromide. In contrast, two previous studies failed to demonstrate any benefit when glu-cagon hydrochloride was administered prior to CT colonography (Yee et al. 1999; Morrin et al. 2002).
While the authors would recommend routine use of hyoscine butylbromide prior to CT colonography, some caution needs to be exercised prior to administration. Glaucoma, cardiac ischaemia and urinary retention may all be precipitated and minor self limiting effects of dry mouth and blurred vision are also associated. Consequently, patients should be questioned about any relevant past medical history and advised not to drive for a short time following administration.
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